Equipment for cleaning the tube sheet in the secondary section of a steam generator that includes a heat exchanger with an enclosure, in whose lower portion is located a tube sheet which divides the circuits for a primary and a secondary medium from one another, is known from U.S. Pat. No. 4,424,769. On the primary side, tubes open into the tube sheet, which, combined in a U-shaped bundle, extend into the space through which the secondary medium flows. The housing has closable service openings, such as hand holes and inspection ports, through which spacing plates for the tubes in the tube bundle, a tube lane between the sides of the tube bundle and tube columns between the individual tubes, can be accessed. A flat nozzle head is used to clean the pipe assembly; it is connected with two or more tubes mounted on top of one another to store a cleaning liquid. These tubes arranged on top of one another are sheathed in such a manner that a strip-shaped guiding element with a rectangular cross section is formed. At one of the hand holes, there is fastened a guide and drive unit, by means of which the strip-shaped guiding element with the nozzle head is inserted into a tube lane or a tube column of the steam generator. In this case, the nozzle head is moved step by step, so that the cleaning fluid, which emerges from the nozzle at a very high pressure of at least 200 bar, is only sprayed into the respective tube columns and not on the tubes. Since the nozzle head and the strip-shaped guiding element are designed to be very narrow, the nozzle head can also be introduced into the tube column at right angles to the tube lane, and the tube sheet can be cleaned on either the x- or the y-axis. The particles removed are drawn off by suction at the periphery between the bundle and the crossbaffle of the heat exchanger by tubes inserted there. The tubes that feed the cleaning fluid are sheathed in such a manner that there is a rigid feed line in the vertical direction and a flexible feed line in the horizontal direction. Nevertheless, there is no sure way of preventing the strip-shaped guiding element with the spray head attached to its free end from bending or twisting in the wide tube lane in an undesirable manner. In this familiar embodiment, a discharging propulsion mechanism is provided at the service opening, which consists of a large number of driven and undriven rollers, which bend and guide the feedline in the horizontal plane.
Equipment to clean off the deposits on the tube side of a steam generator is already known from U.S. Pat. No. 4,273,076. In it, a nozzle head is mounted on a rigid lance, which is inserted through the hand hole into the tube lane of the steam generator and which holds the nozzle head in any desired position. To drain off the fluid/sludge mixture, there are used a suction tube inserted in a hand hole and a tube located in an opposite hand hole, which ejects a washing fluid that generates a peripheral flow to the suction tube. In this familiar embodiment, there must be sufficient space outside the steam generator to permit the lance to be inserted into the tube lane. It is not possible to insert the lance into the tube column transversely to the tube lane.
The purpose of the invention is to describe a process and equipment with which service work can be performed on the secondary section of heat exchangers when the access is restricted, for example, because there is only a limited free space outside a service opening (hand hole or inspection port).
In addition, it should be possible to introduce a head equipped with a nozzle, a tool or a probe through a very small port--for example, one smaller than or equal to 51 mm--in a heat exchanger and to reach interior components, for example, a web plate in the heat exchanger. When the head is moved forward in the tube bundle, it must maintain a stable position. In addition, the equipment should permit the tube columns to be cleaned from the tube lane in the x-direction and from the middle tube column outward in the y-direction with one and the same head.